1. Field of the Invention
This invention relates to valve safety devices, and more particularly to a safety device for use with a relief valve having a controlled disk type of closing member.
2. Background of the Invention
Relief valves are widely employed throughout many industries to relieve the pressure in containers such as storage tanks, boilers and pipelines to prevent damages to these containers due to excessive pressures. Some of the simpler relief valves employ a spring to bias a diaphragm over an opening to retain gas or fluid in the container until the inside pressure reaches a predetermined value, then allows the diaphragm to move away from the opening to relieve the excessive pressure. More accurate control of the value of inside pressure can be obtained by using a relief valve without a spring and employ a pilot valve to control the opening and closing of the diaphragm. Such a combination is disclosed in the U.S. Pat. No. 3,592,224 issued to Bois on July 1971, and a device of this type is diagrammatically shown in FIG. 1. Such a device affords many advantages, especially opening and closing of the valve corresponding to very precise pressure values, which may be very close to the predetermined opening value. Accordingly, it is desirable to substitute such types of valves for the spring biased valves in appliances where precision is of importance.
Nevertheless, owing to the number, the precision required and the fragility of the constituent parts, of such an apparatus, valves with a diaphragm-controlled disk are less robust than the spring biased valves, which are simpler, and the controlled disk valves have the characteristic of remaining open if the diaphragm happens to be pierced or else damaged.
Accordingly, it is an object of the present invention to provide a safety device for a controlled disk valve which enables, at least temporarily, such a valve to be put again in use, if for any reason its normal working is no longer ensured.
Particularly, it is another object of the present invention to provide a device which can be fitted on an existing diaphragm-controlled disk valve, in a simple way, which gives value to a previously existing material.